Often, the exact location of a surface of a workpiece is needed in order to allow a machine to accurately operate on the workpiece. For instance, in the field of phased array transducers, the determination of the exact location of a transducer's surface is crucial. FIG. 1 provides an example of a transducer 105 that has a surface diced (i.e., cut) into a number of kerfs 110 (i.e., slots 110) by a saw blade. The width of the saw blade determines the width of the diced kerfs.
In addition, the operation of the saw blade determines the depth of each kerf. Moreover, uniform kerf depths are crucial for establishing consistent acoustic response throughout a transducer. The consistency of the kerf depths depends on the transducer surface position that is supplied to the dicing machine. For example, if the dicing machine is programmed for a greater or lesser height than the actual transducer height, the dicing machine will dice kerfs that are respectively too shallow or too deep. Therefore, the accurate determination of the transducer surface position is crucial for the proper operation of the transducer, because the dicing machine needs accurate surface position data to produce consistent kerf depths, which provide consistent acoustic response throughout a transducer.
One prior art method for supplying surface position information to the dicing machine involves manually (1) measuring the height of a transducer at a finite number of random points, (2) calculating an average transducer height, and (3) entering the average transducer height into the dicing program. Since no two transducers are the same, custom measurements, calculations, and software modifications have to be performed for each transducer. Therefore, this average height calculation method is rather time consuming.
Furthermore, this prior art technique is inadequate for a transducer whose height substantially varies along its surface. Finally, this prior art method is susceptible to (1) transducer mounting errors (e.g., errors due to debris underneath a portion of the transducer); (2) human errors (e.g., errors in calculating the average height value or in programming the equipment); (3) mounting unit errors (e.g., errors due to the expansion or contraction of the mounting unit); and (4) blade wear errors (e.g., errors due to the gradual reduction of the blade diameter).
U.S. Pat. No. 4,954,022 discloses another prior art method for determining the position of a surface of a workpiece. Under this approach, "in order to assure uniform depth cuts which are made at a predetermined angle to the surface, the workpiece is insulated from the machine tool, and the workpiece and the tool of the machine tool are connected to an electric circuit which senses the electrical contact between the workpiece and the tool and thereby records the sensed or exact position of the surface of the workpiece." Column 2, lines 36-43. Unfortunately, this prior art approach requires the workpiece to be connected to the power supply. Establishing this connection can be difficult depending on the nature of the workpiece (e.g., the size and shape of the workpiece). In addition, this prior art method requires an entirely conductive workpiece, because it connects the workpiece to the power supply.
U.S. Pat. No. 4,826,370 discloses another prior art method for determining the position of a surface of a workpiece. In particular, this patent discloses an indicator device which on one side contacts the workpiece and on another side contacts the machine tool, in order to establish a circuit between the workpiece, the machine, the machine tool, and a power supply. Thus, this prior art method also requires an entirely conductive workpiece to be connected to the power supply.
Consequently, there is a need in the art for a method and apparatus for determining the position of a surface of a workpiece that is not connected to a power supply and is not entirely conductive. There is also a need in the art for a method and apparatus for accurately determining transducer height values in real-time, in order to obtain uniform kerf depths, which thereby establish consistent acoustic response throughout the transducer.